Global precipitation variability from 1940 to 2009 contradicts models

Media release received from the American Geophysical Union on October 29, 2012:

Global precipitation variability decreased from 1940 to 2009

One of the strongly held assumptions of climate change is that the variability of precipitation will grow with an increase in temperature. Storms will become heavier but less frequent. Flash floods and droughts will increase. Regions that see extensive rainfall will get even more while arid regions will dry out. These projections stem from the way temperature affects precipitation patterns in global models.

However, drawing on seven databases representing global monthly mean precipitation values, Sun et al. find that from 1940 to 2009 global overland precipitation variability actually decreased. In addition, they find that the changes in precipitation patterns that did occur led to a redistribution of rainfall such that on average wet areas and seasons got drier, and dry areas and seasons got wetter.

The authors’ findings stem from a novel interpretation of existing precipitation databases that enabled them to separate the overall precipitation variability into temporal and spatial components. They find that, in agreement with previous research, some regions saw increases in the temporal variability of precipitation. These increases were offset by decreases in other regions and concurrent changes in spatial variability. They find that precipitation increased in mid and high latitudes but decreased near the equator and in the subtropics.

The authors suggest that although precipitation variability may increase with rising carbon dioxide, the overall decreasing trend is driven by the effects of atmospheric aerosols. They suggest that aerosol emissions generally dampen precipitation variability in heavily emitting regions, leading to a net decline in global land precipitation variability over the study period.

Authors:
Fubao Sun and Graham D. Farquhar: Research School of Biology, Australian National University, Canberra, ACT, Australia, and Australian Research Council Centre of Excellence for Climate System Science, Sydney, New South Wales, Australia;

Michael L. Roderick: Research School of Biology and Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia, and Australian Research Council Centre of Excellence for Climate System Science, Sydney, New South Wales, Australia.

I agree that in a warming global trend – arid regions will receive more precipitation and thereby reduce desertification. It is the greening effect of a warming global trend.

But to claim overall precipitation will not increase, seems to contradict Wentz et al empirical evidence of 6.5%/deg C increase in absolute humidity and precipitation. It also seems to contradict logic. As the globe warms, sea levels must rise, giving us an increased ocean surface area (increased evaporate surface), which with higher temps MUST translate into increased rainfall, and further greening.

If we cannot detect this increase in precipitation, one must then answer the question: Where is this extra moisture going?? GK

What are these people using actual measurements?What was that infamous line about, if the data contradicts the mode ,we will defer to the model. Sarc aside this seems a little fuzzy, will wait for more details.

Interesting, nature would tend toward an equilibrium. A very old school idea. I have always found it strange that none of the models ever seem to deal well with this tendency. I suspect it is less a math problem then one of ignorance and hubris.

G. Karst says: October 29, 2012 at 9:01 am
[If we cannot detect this increase in precipitation, one must then answer the question: Where is this extra moisture going?]
If we cannot detect this increase in precipitation, one must then answer the question: Is it warmer now than it was in 1940?
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[As the globe warms, sea levels must rise, giving us an increased ocean surface area (increased evaporate surface)]
Given the slope of shoreline, what is the relationship between volume and surface area of open water on Earth?
—
[As the globe warms, sea levels must rise]
This would explain the lack of recent sea level rise.

1) The prior warming occurred from top-down, solar heating. Today’s warming is from bottom up: the oceans are warmer. Apples and oranges.

2) The prior precipitation occurred during a time the world was “in balance”. We are out of balance now, and so chaos rules. See-sawing is an increase in extremes and a quality of chaos. Apples and oranges.

The base hypothesis of warmer world = heavier/more frequent droughts and storms is itself a silly one. What drives storms and droughts isn’t temperature, it is temperature difference. The Earth is colder when the equatorial region is hotter and the polar areas is colder, because the equatorial zone has a larger area and radiates from that area like T^4. The Earth is warmer when the temperatures are more homogeneous for the same reason. Warmer earth due to more uniform temperatures (all balancing the same insolation) decreases the temperature differences that drive “weather”.

In the end, the world’s climate is a heat engine, and like all heat engines it runs between a hot and cold reservoir. The hot reservoir is the sun, the cold reservoir is outer space. Along the way, the heat energy flows/is driven from hotter to colder by many processes. Convection and bulk transport of both oceanic water and atmosphere involves pressure variation associated with warming and cooling and flow modulation by the “coriolis force” caused by the Earth as a rotating (non-inertial) reference frame. Make the whole system have a uniform temperature and you have NO weather, not until you warm one place and cool another so air in one place uplifts and expands and in another falls and compresses, to create a wind flowing in between and being deflected by rotation.

Nowhere is that more beautifully illustrated than in the mechanisms that drive hurricanes, including the current “perfect storm” hurricane. It is the contrast between the warm gulf stream water and the cold air at TOA that permits the creation of a vast area of inflowing air over the surface of the ocean, picking up heat and humidity, to the eye of the hurricane where it is rapidly lifted up to the TOA to outflow, cool, and rain down, releasing the heat that it picked up to the air the moisture leaves behind. Inflowing cold air will simultaneously disrupt this process (by reducing the energy difference that drives it) and increase its residual power over a broad area as it interacts with the energy charged, humid air already present. “Interesting” times, but not caused by global warming.

Even with Sandy’s landfall as a not-quite cat 1 hurricane, it looks pretty likely that 2012 will extend the all time record since a major hurricane made landfall in the US still further. Indeed, I’m trying to remember if ANY hurricanes were actually hurricane at landfall this year. I’m thinking not… but too lazy to look them up. 2012 could be a year of “only tropical storms”.

the overall decreasing trend is driven by the effects of atmospheric aerosols. They suggest that aerosol emissions generally dampen precipitation variability in heavily emitting regions, leading to a net decline in global land precipitation variability over the study period.

They (aerosols) do, but note the shift around 1976 from declining variability to pretty much flat, when the catalytic converter was mandated in the USA and became standard in much of the world shortly afterwards.

A pet peeve of mine is any discussion of aerosols and global averages is meaningless, as aerosol trends can differ greatly over even a few kilometers.

They should be comparing precipitation and actual aerosol measurements at a location. But that would be a career limiting/ending move by any aspiring climate scientist. So, we have a complete absence of studies comparing actual aerosol measurements and temperature, precipitation, etc at a location (excepting a few comparing aerosols and the pretty much climatically meaningless DTR).

Did models project an increase in P over the period 1940-2009? I seem to recall these projections where about the future. The abstract from the paper bears little resemblance to your conclusion.

“In our warming climate there is a general expectation that the variability of precipitation (P) will increase at daily, monthly and inter-annual timescales. Here we analyse observations of monthly P (1940–2009) over the global land surface using a new theoretical framework that can distinguish changes in global P variance between space and time. We report a near-zero temporal trend in global mean P. Unexpectedly we found a reduction in global land P variance over space and time that was due to a redistribution, where, on average, the dry became wetter while wet became drier. Changes in the P variance were not related to variations in temperature. Instead, the largest changes in P variance were generally found in regions having the largest aerosol emissions. Our results combined with recent modelling studies lead us to speculate that aerosol loading has played a key role in changing the variability of P.”

Nowhere do Sun, et al say their results contradict climate models. Read the paper. It’s very interesting, but Anthony misrepresents not only the conclusions of this work; but does a disservice to their earlier work [such as Sun, et al (2006)].

Anthony, in the past you’ve “snipped” my comments for breaching your protocol regarding posting under more than one name. I have no idea why my comments sometimes appear under my name, while at others they appear under my company name. No subtrerfuge, simply something to do with WordPress and Gravitar. My name is John Parsons. My company is ATARS, Inc.

I understand your point, however, I was trying to point out that any climate optimum must be accompanied by increased evaporation and precipitation. You are probably just as correct to say: if there is no increase in precipitation, then there has been no GW. However, some greening has been observed and the final chapter has yet to be written.

Sustained cooling will also demonstrate the principal clearly by increasing desertification, increasing sequestered ice, and shrinking sea surface area, with a correlated decrease in precipitation. No, I don’t know the magnitude of surface area change, only that it is prime with evaporation rate calculations and that small sea level changes will result in large area additions (There is a lot of shoreline). Relative to total effect on evaporate and precipitation, go figure. GK

G. Karst says: October 29, 2012 at 8:09 pm
However, some greening has been observed
no increase in precipitation.

Could be that the increase in vegitation is dew to non-preciitation related moiture cycling in local areas and boundries, a more steady temperature that reduced wind and had wamer nights might be a factor. Cloud cover would also reduce the amount of evaporation but I’m a bit foggy on the details.

These projections stem from the way temperature affects precipitation patterns in global models.

These projections stem from designer catastrophes. Whatever natural event a region is most afflicted by, will get worse.
Americans are afraid of hurricanes and twisters. Will get worse.
Aussies are afraid of droughts and the Great Barrier Reef being damaged. More droughts and the GBR stuffed.
Africans fear famine and disease. Guess what?
Europeans…well…they’re not afflicted with severe weather as badly as other continents. So they tug at the heart strings with Polly Berras being wiped out.

Recent Earth observations support it contributed because precipitation involves a mechanism involving latent heat lost to the atmosphere. Thunderstorms release huge amounts of energy channeled out of the atmosphere. The reduction in precipitation combines with the reduction in global low level clouds and increasing sunshine hours observed in regions.

In rereading everything on this thread during the last time out you issued me, and after reading the actual paper being discussed here (Sun et al.), it is clear that atarsinc nailed it with his comment shown below:

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atarsinc says: October 29, 2012 at 7:12 pm
Here’s a link to the paper: http://www.agu.org/pubs/crossref/2012/2012GL053369.shtml.
Nowhere do Sun, et al say their results contradict climate models. Read the paper. It’s very interesting, but Anthony misrepresents not only the conclusions of this work; but does a disservice to their earlier work [such as Sun, et al (2006)].
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In your summary of the paper at the top of this thread, your title “Global precipitation variability from 1940 to 2009 contradicts models” does clearly seem to be misleading and, furthermore, it appears that it was intentionally so because at the very end of your summary you add the correct statement:

“The authors suggest that although precipitation variability may increase with rising carbon dioxide, the overall decreasing trend is driven by the effects of atmospheric aerosols. They suggest that aerosol emissions generally dampen precipitation variability in heavily emitting regions, leading to a net decline in global land precipitation variability over the study period.”

As you know and as has been evidenced throughout this tread people often read only titles and can easily be mislead by them. So perhaps you could explain your title? I don’t get it – unless it was just an intentional attempt to mislead, as atarsinc suggested.